Eastern filbert blight on hazelnut — symptoms and treatment

Severity: high

What is Eastern filbert blight

Eastern filbert blight is caused by Anisogramma anomala, a fungus that lives inside the wood of hazelnut and kills branch by branch. It can kill hazelnut trees within a few years. Its high severity rating is earned: this is not a cosmetic leaf problem you can spray away, but a canker disease that must be cut out of the tree.

Symptoms

The tell-tale sign is on the bark, not the leaves. Look for sunken elliptical cankers running lengthwise along branches, and on their surface, rows of black stromata — small, hard bumps erupting through the bark in neat lines. Nothing else on a hazelnut looks quite like those rows. Above the canker the branch dies: leaves yellow, wilt and hang on dead wood, and the dieback stands out against healthy growth around it. Each season the canker extends further and new cankers form elsewhere in the tree, until the tree is hollowed out limb by limb.

Key signs:

• Early: sunken elliptical cankers on branches, easy to miss under leaves
• Early: rows of black stromata erupting through the bark
• Advanced: branch dieback above the cankers, with dead leaves clinging
• Advanced: multiple cankers throughout the canopy, tree death if untreated

Bacterial blight also causes dieback and cankers, but produces yellow-haloed leaf spots and no black stromata — the rows of black bumps are the deciding feature.

Causes and conditions

Spores are released from the black stromata in wet weather and carried by wind and rain splash to new hazelnut wood, where they infect actively growing shoots. Infection happens in spring, while shoots are elongating and the tissue is still soft — that narrow window is the whole disease. From there the fungus grows unseen inside the bark before cankers and stromata break the surface, which is why an orchard can look clean and already be infected. Wet springs favour it, and wild or neglected hazelnuts nearby act as a permanent spore reservoir.

Treatment

Resistant varieties and scouting — cultural

At planting and throughout. Plant resistant varieties. Scout regularly for cankers. Remove infected branches 1 m below cankers — the fungus extends beyond the visible canker, so cutting at the edge leaves it in the tree. Take the prunings out of the orchard and destroy them so they cannot keep releasing spores.

Chlorothalonil — chemical

Bud break to shoot elongation. Apply fungicide sprays from bud break through early shoot elongation (8 weeks). Critical prevention window. Sprays protect vulnerable new growth while spores are landing; they do nothing for fungus already inside the wood. Pre-harvest interval: 14 days. Pesticide registrations vary by country — check local approval before use.

Prevention

• Plant resistant varieties — the single most effective decision, made once at planting.
• Scout every year, looking at bark rather than leaves, and mark cankered limbs.
• Prune out infected wood 1 m below the canker and destroy it away from the orchard.
• Remove wild or abandoned hazelnuts near the orchard, which serve as spore sources.
• Buy clean, certified planting stock and inspect new trees before planting.

Frequently asked questions

Is it contagious to my other hazelnut trees? Yes. Spores blow from the black stromata to nearby trees in wet weather. One neglected cankered tree can infect a whole planting — removing infected wood matters for the orchard, not just that tree.

Can I save an infected tree? Sometimes, if you catch it early and are ruthless. Cut every infected limb 1 m below the canker and keep scouting. Once cankers are spread through the main framework, replacement with a resistant variety is the realistic answer.

When should I spray? Only in the critical window — bud break through early shoot elongation, when new growth is susceptible and spores are landing. Sprays outside that window are wasted, because infection does not happen then.